Reactive ion etching of yttrium oxide thin films was investigated using and inductively coupled plasmas. For all gas combinations, with the exception of , the etch rate was found to be similar, indicating a primarily physical etch process, enhanced in by an additional chemical-etching component. The highest observed etch rate was 53 nm/min in , suitable for controlled etching of optical ridge waveguide structures several hundred nm in height. Overall, the surface quality of the etched films was the highest after etching in plasmas, indicating a trade-off in etch rate and film quality between the various process gases. Preliminary selectivity measurements show that Ni is a suitable material for etch-masking of high resolution structures in .